Dressage first and foremost. Both you and she need to learn to work together, your form and position in the saddle, and incorporating that through your horses movement and energy, to get her on her hind end, back rounded up into your seat, light, soft and lifted.
You have to have Dressage first, before the jumping. Jumping is dressage with speed bumps.
Right now, she is going around heavy on her front end, probobly leaning into your hands, flat and heavy - but to fix that, you must fix your seat, legs, core, upperbody, hand carraige, shoulders. Our horses reflect what we do in the saddle, if you are out, so is your horse. If you aren't aiding your horse to get off of their front end, then how is she supposed to do it herself?
This is a copy and a paste from a post I've made quite a few times in this forum when people post about having the same problem:
If you give your horse something to lean into, he will take it 100% of the time. Especially OTTB's.
That is why you must learn to ride, SEAT into LEGS into HANDS to SOFTEN
Let me ask you, how are you riding your horse right now? Are you riding all hands, face first and totally leaving your seat out of the picture? You cannot do this, regardless if you are doing Dressage or Jumping.
Forget your horses face, and focus on his hind end. Forget your horses face, and focus on getting him off of his forehand. Forget his face and focus on rounding him up into your aids and establishing a rhythm - how do you do this?
Dressage and proper body position to be an effective rider, to make your horse an effective mount.
Let me tell you my experience.
When I first started riding my now OTTB Nelson - he was great out on the trails, great in the Dressage Ring, but when it came to jumping, he was super powerful, very strong and extremely forward.
I remember jumping a small CC fence with him, and by the time I got him back down and under control, we were already clear over on the other side of the CC field. Rediculous.
So, at that time, Dorothy Crowell was coming to my barn for our Local Pony Club to give a Clinic *Dorothy is a CIC**** and CCI**** Eventer, who has represented the U.S.A in the Olympics* so I signed up to ride in her clinic because I wanted and needed help with Nelson's power over fences.
She set up a grid, 3 jumps * I cannot quite recall the striding now * but the first fence was an x rail I believe, to a 3 or 4 stride, to an Oxer, to a 4 or 5 stride and to a verticle.
Nelson and I approached the first fence quiet and at a nice rhythmic pace. The moment he landed from that first fence, he took off. That 3 or 4 stride became a 2 or 3 stride and the 4 or 5 stride became a 3 or 4 stride. I remember I was standing in my irons pulling on his face.
She stopped us and pulled us aside. The first thing she told me was "you give your horse something to lean into, he'll take it" and that is exactly what Nelson did. I pulled on the reins, he said "thank you!" took it and leant into it and was gone.
She taught me Seat Into Legs Into Hands To Soften.
Your seat controls your horses hind end. You establish a rhythm with your seat. You establish impulsion with your seat - you activate that hind end with your seat.
You tense your seat - your horse becomes tense. You relax your seat, your horse relaxes. You slow your seat, your horse slows down to you. You quicken your seat, your horse quickens.
It comes from your seat. You must learn to ride on all 3 points *two seat bones, and crotch*
Remain over his center of gravity. Do not lean forward, do not lean back - remain over his center.
The moment you get what you are asking for from your seat, you activate your legs. Your legs continue that rhythm you've created through your seat, and your legs lift the horses ribs/spine up into your seat.
Your hands come into play lastly. Your outside rein must be there to allow that energy to recyle. You do not want that energy to gush out your horses front end. But they are soft, supple and must be giving at all times.
I was shown this by Dorothy and I immediately had a different horse.
She had me approach the first fence, when I was a stride away, she had me release my arms, sit and close my legs. The moment we landed I had to sit back down, slow my seat down, close my legs and put him in check. Then a stride away, I released my arms and gave him his face.
If he tried to speed up at all, I was to make him to exercises - whether it be figure 8's or serpentines or circles, I had to work on slowing my seat down, lifting his ribs and bring him back down under me.
Then we would repeat the fences.
I can now ride my TB over any course with a rubber snaffle if I chose. My horse comes down to me at all times.